1. Field of the Invention
The present invention relates to a catheter guide wire for use in guiding a catheter, and in particular, to such a catheter guide wire using a shape memory alloy with pseudo elasticity.
2. Description of the Prior Art
The catheter guide wire is for guiding the catheter through cavities such as blood vessels within a body. The catheter guide wire is inserted into a cavity of the body and is steered therethrough so that its end arrives at a destination position. Then, the catheter is fitted onto the catheter guide wire and is guided through the blood vessel by the catheter guide wire to the destination position.
Since a blood vessel has various branches in different directions within the body, the catheter guide wire must be steerable through the blood vessels so as to reach the destination position.
It is well known in the prior art to make the catheter guide wire of a shape memory alloy so as to use pseudo elasticity of the shape memory alloy for the steerability of the wire. Reference is made to JP-A-63-171570 (Reference I), JP-A-64-49570 (Reference II) and others.
It is also known to use the shape memory alloy for the catheter itself and other medical appliances in JP-A-60-100956 based on U.S. patent application Ser. No. 541,852 filed on Oct. 14, 1983 (Reference III).
A typical shape memory alloy is Ti-Ni alloy as shown in all of the Reference. Cu-Zn-Al, Cu-Al-Ni, Fe-Mn alloys are also known as the shape memory alloy as shown in Reference I.
Those shape memory alloys may have the pseudo elasticity at a temperature of about 37.degree. C. by controlling ingredients and their amounts of the alloy composition and/or a temperature for heat-treating the alloy.
The pseudo elasticity is characterized by a stress-strain curve having a generally rectangular hysteresis loop wherein strain gradually increases with increase of stress and rapidly and suddenly increases at an elevated stress (yield point) while strain gradually reduces with reduction of stress and rapidly and suddenly reduces at a reduced stress, as shown at 1 in FIG. 1 of Reference I, in FIG. 6 of Reference II, and in FIGS. 1 and 2 of Reference III.
Although the catheter guide wire using the shape memory alloy is steerable, it is difficult to form the end portion of the wire into a desired shape, because the catheter guide wire has the elasticity. Accordingly, it is necessary clinically to store a plurality of catheter guide wires having different end shapes which are called, for example, a J-shape type, an angular type, and others. However, if it is possible to readily plastically bend, deform, or work the end of the catheter guide wire into a desired shape, a single catheter guide wire can be adapted for various conditions of the catheter guide wire end shape.
Further, since the catheter guide wire using the shape memory alloy has the pseudo elasticity, it is readily elastically deformed by any force applied to the guide wire. Therefore, transmission of the force is insufficient through the catheter guide wire to the end portion from a portion away from the end portion, so that insertion force and/or rotating force applied to the catheter guide wire is hardly transmitted to the end portion. This means the guide wire does not have a good steerability.